Sounding packet format for long range WLAN

ABSTRACT

In a method for generating a null data packet (NDP) sounding packet for transmission via a communication channel, a signal field and one or more long training fields are generated. The signal field and the long training fields are modulated using a plurality of orthogonal frequency division multiplexing (OFDM) symbols. Symbol duration of each OFDM symbol of the plurality of OFDM symbols is at least 8 μs. The NDP sounding packet is generated to include the plurality of OFDM symbols. The NDP sounding packet omits a data payload portion.

CROSS-REFERENCES TO RELATED APPLICATIONS

This disclosure claims the benefit of U.S. Provisional PatentApplication No. 61/490,465, entitled “Sounding Packet Format for 11ahand 11af,” filed on May 26, 2011, and U.S. Provisional PatentApplication No. 61/494,349, entitled “Sounding Packet Format for 11ahand 11af,” filed on Jun. 7, 2011, the disclosures of both of which arehereby incorporated by reference herein in their entireties.

FIELD OF THE DISCLOSURE

The present disclosure relates generally to communication networks and,more particularly, to long range low power wireless local area networks.

BACKGROUND

The background description provided herein is for the purpose ofgenerally presenting the context of the disclosure. Work of thepresently named inventors, to the extent it is described in thisbackground section, as well as aspects of the description that may nototherwise qualify as prior art at the time of filing, are neitherexpressly nor impliedly admitted as prior art against the presentdisclosure.

Development of wireless local area network (WLAN) standards such as theInstitute for Electrical and Electronics Engineers (IEEE) 802.11a,802.11b, 802.11g, and 802.11n Standards has improved single-user peakdata throughput. For example, the IEEE 802.11b Standard specifies asingle-user peak throughput of 11 megabits per second (Mbps), the IEEE802.11a and 802.11g Standards specify a single-user peak throughput of54 Mbps, the IEEE 802.11n Standard specifies a single-user peakthroughput of 600 Mbps, and the IEEE 802.11ac Standard (now beingfinalized) specifies a single-user peak throughput in the gigabits persecond (Gbps) range.

Work has begun on two new standards, IEEE 802.11ah and IEEE 802.11af,each of which will specify wireless network operation in sub-1 GHzfrequencies. Lower frequency communication channels are generallycharacterized by better propagation qualities and extended propagationranges compared to transmission at higher frequencies. In the past,sub-1 GHz ranges have not been utilized for wireless communicationnetworks because such frequencies were reserved for other applications(e.g., licensed TV frequency bands, radio frequency band, etc.). Thereare few frequency bands in the sub 1-GHz range that remain unlicensed,with different specific unlicensed frequencies in different geographicalregions. The IEEE 802.11ah Standard will specify wireless operation inavailable unlicensed sub-1 GHz frequency bands. The IEEE 802.11afStandard will specify wireless operation in TV White Space (TVWS), i.e.,unused TV channels in sub-1 GHz frequency bands.

SUMMARY

In various embodiments described below, a sounding packet used forsounding a communication channel is generated in accordance with aphysical layer (PHY) sounding packet format described herein. In someembodiments, the sounding packet is generated according to one ofseveral PHY sounding packet formats depending on the mode in which thesounding packet is to be transmitted.

In one embodiment, a method for generating a null data packet (NDP)sounding packet for transmission via a communication channel includesgenerating a signal field and generating one or more long trainingfields. The method also includes modulating the signal field and thelong training fields using a plurality of orthogonal frequency divisionmultiplexing (OFDM) symbols, wherein symbol duration of each OFDM symbolof the plurality of OFDM symbols is at least 8 μs. The method furtherincludes generating the NDP sounding packet to include the plurality ofOFDM symbols, wherein the NDP sounding packet omits a data payloadportion.

In other embodiments, the method includes any combination of one or moreof the following elements.

Generating the one or more long training fields includes generating atleast one of the one or more training fields to include pilot tones andnon-pilot tones.

The method further includes mapping the non-pilot tones to a pluralityof multiple spatial or space-time streams using a mapping matrix, andmapping the pilot tones to the plurality of multiple spatial orspace-time streams using a column of the mapping matrix.

The column of the mapping matrix used to map pilot tones to the multiplespatial or space-time streams is the first column of the mapping matrix.

The method further comprises mapping the non-pilot tones to a pluralityof multiple spatial or space-time streams using a mapping matrix, andmapping the pilot tones to the plurality of multiple spatial orspace-time streams using a row of the mapping matrix.

The row of the mapping matrix used to map pilot tones to the multiplespatial or space-time streams is the row column of the mapping matrix.

The NDP sounding packet is formatted according to a PHY preamble formatof a regular packet. The method further includes setting each of one ormore subfields in the signal field to a respective first value to signalto a receiving device that the NDP sounding packet is a sounding packetand not a regular data unit.

The one or more subfields include at least one of i) a length subfieldand ii) a modulation and coding scheme (MCS) subfield.

The method further includes setting the length subfield to a value ofzero to signal to the receiving device that the NDP sounding packet is asounding packet.

The method further includes further comprising setting the MCS subfieldto a value other than a valid MCS value to signal to the receivingdevice that the NDP sounding packet is a sounding packet, wherein thevalid MCS value is a value used to indicate an MCS for a regular dataunit.

In another embodiment, an apparatus comprises a network interfaceconfigured to generate a signal field and generate one or more longtraining fields. The network interface is also configured to modulatethe preamble portion using a plurality of orthogonal frequency divisionmultiplexing (OFDM) symbols, wherein symbol duration of each OFDM symbolof the plurality of OFDM symbols is at least 8 μs. The network interfaceis further configured to generate the NDP sounding packet to include theplurality of OFDM symbols. The NDP sounding packet does omits a datapayload portion.

In other embodiments, the apparatus includes any combination of one ormore of the following features.

The network interface is configured to generate at least one of the oneor more training fields to include pilot tones and non-pilot tones.

The network interface is further configured to map the non-pilot tonesto multiple spatial or space-time streams using a mapping matrix, andmap the pilot tones to multiple spatial or space-time stream a column ofthe mapping matrix.

The network interface is configured to map pilot tones to multiplespatial or space-time streams using the first column of the mappingmatrix.

The network interface is further configured to map the non-pilot tonesto multiple spatial or space-time streams using a mapping matrix, andmap the pilot tones to multiple spatial or space-time stream a row ofthe mapping matrix.

The network interface is configured to map pilot tones to multiplespatial or space-time streams using the first row of the mapping matrix.

The NDP sounding packet is formatted according to a PHY preamble formatof a regular packet.

The network interface is further configured to set each of one or moresubfields in the signal field to a respective first value to signal to areceiving device that the NDP sounding packet is a sounding packet andnot a regular data unit.

The one or more subfields used to signal to the receiving device thatthe NDP sounding packet is a sounding packet include at least one of i)a length subfield and ii) a modulation and coding scheme (MCS) subfield.

The network interface is configured to set the length subfield to avalue of zero to signal to the receiving device that the NDP soundingpacket is a sounding packet.

The network interface is configured to set the MCS subfield to a valueother than a valid MCS value to signal to the receiving device that theNDP sounding packet is a sounding packet, wherein the valid MCS value isa value used to indicate an MCS for a regular data unit.

In still another embodiment, a method includes generating a null datapacket (NDP) sounding packet according to a first PHY sounding packetformat specified by a communication protocol when the NDP soundingpacket is to be transmitted in a normal PHY mode. The method alsoincludes generating the NDP sounding packet according to a second PHYsounding packet format defined by the communication protocol when theNDP sounding packet is to be transmitted in an extended range PHY mode.

In other embodiments, the method includes any combination of one or moreof the following features.

The first PHY sounding packet format is based on a first PHY preambleformat specified by the communication protocol to be included in dataunits transmitted in the normal PHY mode, and the second PHY soundingpacket format is based on a second PHY preamble format specified by thecommunication protocol to be included in data units transmitted in theextended range PHY mode.

The second PHY preamble format is specified for single stream data unitsand wherein the second PHY sounding packet format is specified for multistream sounding packets.

The method further comprises generating a regular data unit thatincludes a data payload portion, wherein the data unit is to betransmitted in the extended range mode, and generating a signal fieldincluding generating a first subfield and a second subfield, wherein thesignal field is to be included in one of i) a preamble of the regulardata unit or ii) the NDP sounding packet to be transmitted in theextended range mode.

The first subfield is a length subfield i) set to a value other than afirst value when the signal field is to be included in the regular dataunit and ii) set to the first value when the signal field is to beincluded in the NDP sounding packet, and the second subfield includes anumber of streams indicator when signal field is to be included in theNDP sounding packet.

The first subfield is a length subfield i) set to a value other than afirst value when the signal field is to be included in the regular dataunit and ii) set to the first value when the signal field is to beincluded in the NDP sounding packet, and the second subfield includes i)a number of streams indicator when the signal field is to be included inthe NDP sounding packet and ii) a scrambler seed value when the signalfield is to be included in the regular data unit.

The first subfield is used to indicate whether the packet is the regulardata unit or the NDP sounding packet, and the second subfield includesi) a length value to indicate a length of the regular data unit when thefirst subfield indicates that the packet is the regular data unit andii) a number of streams indicator when the first subfield indicates thatthe packet is the NDP sounding packet.

The first subfield is a modulation and coding (MCS) subfield. A value ofthe MCS subfield other than a valid MCS value is used to indicate thatthe packet is a sounding packet, wherein the valid MCS value is a valueused to indicate a valid MCS for a regular data unit.

In yet another embodiment, an apparatus comprises a network interfaceconfigured to generate a null data packet (NDP) sounding packetaccording to a first PHY sounding packet format specified by acommunication protocol when the NDP sounding packet is to be transmittedin a normal PHY mode. The network interface is also configured togenerate the NDP sounding packet according to a second PHY soundingpacket format defined by the communication protocol when the NDPsounding packet is to be transmitted in an extended range PHY mode.

In other embodiments, the apparatus includes one or more of thefollowing features.

The second PHY preamble format is specified for single stream dataunits, and wherein the second PHY sounding packet format is specifiedfor multi stream sounding packets.

The network interface is further configured to generate a regular dataunit that includes a data payload portion, wherein the data unit is tobe transmitted in the extended range mode, and generate a signal fieldincluding generating a first subfield and a second subfield, wherein thesignal field is to be included in one of i) a preamble of the regulardata unit or ii) the NDP sounding packet to be transmitted in theextended range mode.

The first subfield is a length subfield i) set to a value other than afirst value when the signal field is to be included in the regular dataunit and ii) set to the first value when the signal field is to beincluded in the NDP sounding packet, and the second subfield includes anumber of streams indicator when signal field is to be included in theNDP sounding packet.

The first subfield is a length subfield i) set to a value other than afirst value when the signal field is to be included in the regular dataunit and ii) set to the first value when the signal field is to beincluded in the NDP sounding packet, and the second subfield includes i)a number of streams indicator when the signal field is to be included inthe NDP sounding packet and ii) a scrambler seed value when the signalfield is to be included in the regular data unit.

The first subfield is set to indicate whether the packet is the regulardata packet or the NDP sounding packet, and the second subfield includesi) a length value to indicate a length of the regular data unit when thefirst subfield indicates that the packet is the regular data unit andii) a number of streams indicator when the first subfield indicates thatthe packet is the NDP sounding packet.

The first subfield is a modulation and coding scheme (MCS) subfield, andthe network interface is configured to indicate that the packet is asounding packet by setting the MCS subfield to a value other than avalid MCS value, wherein the valid MCS value is a value used to indicatea valid MCS for a regular data unit.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of an example wireless local area network(WLAN) 10, according to an embodiment;

FIGS. 2A and 2B are diagrams of a short range orthogonal frequencydivision multiplexing (OFDM) data unit, according to an embodiment;

FIG. 3 is a diagram of a short range OFDM data unit, according toanother embodiment;

FIG. 4 is a diagram of a short range OFDM data unit, according toanother embodiment;

FIG. 5 is a diagram of a short range OFDM data unit, according toanother embodiment;

FIG. 6 is a set of diagrams illustrating modulation of various preamblefields as defined by the IEEE 802.11n Standard;

FIG. 7 is a set of diagrams illustrating modulation of various preamblefields as defined by the IEEE 802.11ac Standard;

FIG. 8A is a diagram of an example null data packet (NDP) soundingpacket, according to an embodiment.

FIG. 8B is an example NDP sounding packet generated according to theexample sounding packet format of FIG. 8A for a case of four antennas,according to an embodiment.

FIG. 9 is a diagram of an example NDP sounding packet, according toanother embodiment.

FIG. 10 is a diagram of an example NDP sounding packet, according toanother embodiment.

FIG. 11 is a diagram of an example NDP sounding packet to be transmittedin an extended range mode, according to an embodiment.

FIG. 12A is a diagram of an example signal field included in an NDPsounding packet and/or in a preamble of a regular data unit, accordingto an embodiment.

FIG. 12B is a diagram of an example signal field included in an NDPsounding packet and/or in a preamble of a regular data unit, accordingto another embodiment.

FIG. 12C is a diagram of an example signal field included in an NDPsounding packet and/or in a preamble of a regular data unit, accordingto another embodiment.

FIG. 13 is a flow diagram of an example method for generating an NDPsounding packet, according to an embodiment.

FIG. 14 is a flow diagram of an example method, according to anembodiment.

DETAILED DESCRIPTION

In embodiments described below, a wireless network device such as anaccess point (AP) of a wireless local area network (WLAN) transmits datastreams to one or more client stations. The AP is configured to operatewith client stations according to at least a first communicationprotocol. The first communication protocol defines operation in a sub 1GH frequency range, and is typically used for applications requiringlong range wireless communication with relatively low data rates (ascompared with “short range” communication protocols discussed below).The first communication protocol (e.g., IEEE 802.11af or IEEE 802.11ah)is referred to herein as a “long range” communication protocol. In someembodiments, the AP is also configured to operate with client stationsaccording to one or more other communication protocols which defineoperation in generally higher frequency ranges and are typically usedfor communication in closer ranges and with generally higher data ratesas compared to the first communication protocol. The closer rangecommunication protocols are collectively referred to herein as “shortrange” communication protocols.

In at least some embodiments, the AP and at least some of the clientstations each include multiple antennas and are configured to utilizetransmit and/or receive beamforming to enhance one or more ofthroughput, range, etc. Additionally or alternatively, in someembodiments, in a technique known as multi user communication, the AP isconfigured to utilize the spatial diversity provided by the multipleantennas by simultaneously transmitting data streams to multiple clientstations. In such embodiments, the AP utilizes knowledge of thecommunication channels between the AP and the multiple client stationsto steer each of the multiple data streams transmitted simultaneously tothe intended user while minimizing interference from the other users. Tothese ends, in various embodiments and/or scenarios, the AP and/or aclient station utilize knowledge of the channel to determine abeamforming or a beamsteering matrix to be applied to signalstransmitted or received via multiple antennas. In some systems,obtaining explicit knowledge of the channel involves a beamformertransmitting known training signals to a beamformee, which thengenerates a measurement of the channel (sometimes referred to as channelstate information or CSI) based on the received training signals.Transmitting such training signals is sometimes referred to as soundinga communication channel, or transmitting a sounding packet.

In some embodiments, the long range communication protocol defines oneor more physical layer data unit formats the same as or similar tophysical layer data unit format defined by one or more of the shortrange communication protocols. In one embodiment, to supportcommunication over a longer range, and also to accommodate typicallysmaller bandwidth channels available at lower (sub 1-GHz) frequencies,the long range communication protocol defines data units having a formatthat is substantially the same as a physical layer data unit formatdefined by a long range communication protocol, but generated using alower clock rate. Similarly, in an embodiment, the long rangecommunication protocol specifies a null data packet (NDP) soundingpacket format that is based on a PHY preamble format specified by ashort range communication protocol, but generated using a lower clockrate. In an embodiment, the AP operates at a clock rate suitable forshort range (and high throughput) operation, and down-clocking is usedto generate a new clock signal to be used for the sub 1 GHz operation.As a result, in this embodiment, an NDP sounding packet that conforms tothe long rage communication protocol maintains a physical layer preambleformat of a data unit that generally conforms to a short rangecommunication protocol (“short range data unit”), but is transmittedover a longer period of time and/or at a slower rate. An NDP packetcomprises a preamble portion and omits a data payload portion.

In one embodiment, in a multi user system, a sounding packet istypically transmitted to each user individually, and, accordingly, inorder to reduce the length of NPD sounding packets, NDP sounding packetformat is based on a single user (SU) preamble format (rather than amulti user (MU) preamble format) specified by a short rangecommunication protocol. Further, in some embodiments, the long rangecommunication protocol specifies one or more extended range modes tofurther extend the communication range between devices (e.g., betweenthe AP and the client stations, or between two client stations). In somesuch embodiments, the long range communication protocol specifies asuitable PHY preamble format for the extended range modes that isdifferent from the PHY preamble format used for normal mode data units.In such embodiments, an NDP sounding packet format for sounding packetstransmitted in the extended range mode is based on the PHY preambleformat specified for the extended range data units. As a result, in thisembodiment, an NDP sounding packet transmitted by an AP or a clientstation is formatted differently depending on the particular mode beingutilized (e.g., normal PHY mode or extended range mode).

FIG. 1 is a block diagram of an example wireless local area network(WLAN) 10, according to an embodiment. An AP 14 includes a hostprocessor 15 coupled to a network interface 16. The network interface 16includes a medium access control (MAC) processing unit 18 and a physicallayer (PHY) processing unit 20. The PHY processing unit 20 includes aplurality of transceivers 21, and the transceivers 21 are coupled to aplurality of antennas 24. Although three transceivers 21 and threeantennas 24 are illustrated in FIG. 1, the AP 14 can include differentnumbers (e.g., 1, 2, 4, 5, etc.) of transceivers 21 and antennas 24 inother embodiments.

The WLAN 10 includes a plurality of client stations 25. Although fourclient stations 25 are illustrated in FIG. 1, the WLAN 10 can includedifferent numbers (e.g., 1, 2, 3, 5, 6, etc.) of client stations 25 invarious scenarios and embodiments. At least one of the client stations25 (e.g., client station 25-1) is configured to operate at leastaccording to the long range communication protocol. In some embodiments,at least one of the client stations 25 (e.g., client station 25-4) is ashort range client station that is configured to operate according toone or more of the short range communication protocols.

The client station 25-1 includes a host processor 26 coupled to anetwork interface 27. The network interface 27 includes a MAC processingunit 28 and a PHY processing unit 29. The PHY processing unit 29includes a plurality of transceivers 30, and the transceivers 30 arecoupled to a plurality of antennas 34. Although three transceivers 30and three antennas 34 are illustrated in FIG. 1, the client station 25-1can include different numbers (e.g., 1, 2, 4, 5, etc.) of transceivers30 and antennas 34 in other embodiments.

In an embodiment, one or both of the client stations 25-2 and 25-3, hasa structure the same as or similar to the client station 25-1. In anembodiment, the client station 25-4 has a structure similar to theclient station 25-1. In these embodiments, the client stations 25structured the same as or similar to the client station 25-1 have thesame or a different number of transceivers and antennas. For example,the client station 25-2 has only two transceivers and two antennas,according to an embodiment.

In various embodiments, the network interface 16 of the AP 14 isconfigured to generate data units conforming to the long rangecommunication protocol and having formats described hereinafter. Thetransceiver(s) 21 is/are configured to transmit the generated data unitsvia the antenna(s) 24. Similarly, the transceiver(s) 24 is/areconfigured to receive the data units via the antenna(s) 24. The networkinterface 16 of the AP 14 is configured to process received data unitsconforming to the long range communication protocol and having formatsdescribed hereinafter, according to various embodiments.

In various embodiments, the network interface 27 of the client device25-1 is configured to generate data units conforming to the long rangecommunication protocol and having formats described hereinafter. Thetransceiver(s) 30 is/are configured to transmit the generated data unitsvia the antenna(s) 34. Similarly, the transceiver(s) 30 is/areconfigured to receive data units via the antenna(s) 34. The networkinterface 27 of the client device 25-1 is configured to process receiveddata units conforming to the long range communication protocol andhaving formats described hereinafter, according to various embodiments.

FIG. 2A is a diagram of a short range OFDM data unit 200 that thenetwork interface 16 of the AP 14 is configured to generate and transmitto the client station 25-4 via orthogonal frequency divisionmultiplexing (OFDM) modulation when operating according to a short rangecommunication protocol, according to an embodiment. In an embodiment,the network interface of the client station 25-4 is also configured togenerate and transmit the short range data unit 200 to the AP 14. Thedata unit 200 conforms to the IEEE 802.11a Standard (and/or the IEEE802.11b Standard) and occupies a 20 Megahertz (MHz) band. The data unit200 includes a preamble having a legacy short training field (L-STF)202, generally used for packet detection, initial synchronization, andautomatic gain control, etc., and a legacy long training field (L-LTF)204, generally used for channel estimation and fine synchronization. Thedata unit 200 also includes a legacy signal field (L-SIG) 206, used tocarry certain physical layer (PHY) parameters of the data unit 200, suchas modulation type and coding rate used to transmit the data unit, forexample. The data unit 200 also includes a data payload portion 208.FIG. 2B is a diagram of example data payload portion 208 (not lowdensity parity check encoded), which includes a service field, ascrambled physical layer service data unit (PSDU), tail bits, andpadding bits, if needed. The data unit 200 is designed for transmissionover one spatial or space-time stream in single input a single output(SISO) channel configuration.

FIG. 3 is a diagram of a short range OFDM data unit 300 that the networkinterface 16 of the AP 14 is configured to generate and transmit to theclient station 25-4 via orthogonal frequency domain multiplexing (OFDM)modulation when operating according to a short range communicationprotocol, according to an embodiment. In an embodiment, the networkinterface of the client station 25-4 is also configured to generate andtransmit the short range data unit 300 to the AP 14. The data unit 300conforms to the IEEE 802.11n Standard, occupies a 20 MHz or a 40 MHzband, and is designed for mixed mode situations, i.e., when the WLANincludes one or more client stations that conform to the IEEE 802.11aStandard (and/or the IEEE 802.11g Standard) but not the IEEE 802.11nStandard. The data unit 300 includes a preamble having an L-STF 302, anL-LTF 304, an L-SIG 306, a high throughput signal field (HT-SIG) 308, ahigh throughput short training field (HT-STF) 310, and M data highthroughput long training fields (HT-LTFs) 312, where M is an integerwhich generally corresponds to a number of spatial or space-time streamsused to transmit the data unit 300 in a multiple input multiple output(MIMO) channel configuration. In particular, according to the IEEE802.11n Standard, the data unit 300 includes two HT-LTFs 312 if the dataunit 300 is transmitted using two spatial or space-time streams, andfour HT-LTFs 312 is the data unit 300 is transmitted using three or fourspatial or space-time streams. An indication of the particular number ofspatial or space-time streams being utilized is included in the HT-SIGfield 308. The data unit 300 also includes a data payload portion 314.

FIG. 4 is a diagram of a short range OFDM data unit 400 that the networkinterface 16 of the AP 14 is configured to generate and transmit to theclient station 25-4 via orthogonal frequency domain multiplexing (OFDM)modulation when operating according to a short range communicationprotocol, according to an embodiment. In an embodiment, the networkinterface of the client station 25-4 is also configured to generate andtransmit the short range data unit 400 to the AP 14. The data unit 400conforms to the IEEE 802.11n Standard, occupies a 20 MHz or a 40 MHzband, and is designed for “Greenfield” situations, i.e., when the WLANdoes not include any client stations that conform to the IEEE 802.11aStandard (and/or the IEEE 802.11g Standard) but not the IEEE 802.11nStandard. The data unit 400 includes a preamble having a high throughputGreenfield short training field (HT-GF-STF) 402, a first high throughputlong training field (HT-LTF1) 404, a HT-SIG 406, and M data HT-LTFs 408,where M is an integer which generally corresponds to a number of spatialor space-time streams used to transmit the data unit 400 in a multipleinput multiple output (MIMO) channel configuration. The data unit 400also includes a data payload portion 410.

FIG. 5 is a diagram of a short range OFDM data unit 500 that the networkinterface 16 of the AP 14 is configured to generate and transmit to theclient station 25-4 via orthogonal frequency domain multiplexing (OFDM)modulation when operating according to a short range communicationprotocol, according to an embodiment. In an embodiment, the networkinterface of the client station 25-4 is also configured to generate andtransmit the data unit 500 to the AP 14. The data unit 500 conforms tothe IEEE 802.11ac Standard and is designed for “Mixed field” situations.The data unit 500 occupies a 20 MHz bandwidth. In other embodiments orscenarios, a data unit similar to the data unit 500 occupies a differentbandwidth, such as a 40 MHz, an 80 MHz, or a 160 MHz bandwidth. The dataunit 500 includes a preamble having an L-STF 502, an L-LTF 504, an L-SIG506, a first very high throughput signal field (VHT-SIG-A) 508, a veryhigh throughput short training field (VHT-STF) 510, M very highthroughput long training fields (VHT-LTFs) 512, where M is an integer, asecond very high throughput signal field (VHT-SIG-B) 514. The data unit500 also includes a data payload portion 516. In some embodiments, thedata unit 500 is a multi-user data unit which carries information tomore than one of the client stations 25 simultaneously. In suchembodiments or scenarios, the VHT-SIG-A field 508 includes informationcommon to all of the intended client stations, and the VHT-SIG-B field514 includes user-specific information for each of the intended clientstations.

FIG. 6 is a set of diagrams illustrating modulation of the L-SIG,HT-SIG1, and HT-SIG2 fields as defined by the IEEE 802.11n Standard. TheL-SIG field is modulated according to binary phase shift keying (BPSK),whereas the HT-SIG1 and HT-SIG2 fields are modulated according to BPSK,but on the quadrature axis (Q-BPSK). In other words, the modulation ofthe HT-SIG1 and HT-SIG2 fields is rotated by 90 degrees as compared tothe modulation of the L-SIG field. As illustrated in FIG. 6, suchmodulation allows a receiving device to determine or auto-detect,without decoding the entire preamble, that the data unit conforms to theIEEE802.11n Standard rather than the IEE802.11a Standard.

FIG. 7 is a set of diagrams illustrating modulation of the L-SIG field,the first symbol of the VHT-SIG-A field, the second symbol of theVHT-SIG-A field, and VHT-SIG-B as defined by the IEEE 802.11ac Standard.The L-SIG field is modulated according to binary phase shift keying(BPSK). Similarly, first symbol of the VHT-SIGA field is modulatedaccording to BPSK. On the other hand, the second symbol of the VHT-SIG-Afield is modulated according to BPSK, but on the quadrature axis(Q-BPSK). The VHT-SIG-B field is modulated according to BPSK, similar tothe L-SIG-field and the first symbol of the VHT-SIG-A field. Suchmodulation allows a receiving device to determine or auto-detect,without decoding the entire preamble, that the data unit conforms to theIEEE802.11ac Standard rather than either one of the IEE802.11a Standardor the IEEE802.11n Standard.

In various embodiments and/or scenarios, long range data units have aphysical layer format the same as or similar to the physical layer dataunit format defined by a short range communication protocol (e.g., aphysical data unit format described above with respect to FIGS. 2-5),but transmitted using a slower clock rate. In such embodiments, thenetwork interface 16 of the AP 14 down-samples or “down-clocks” theclock rate used for generating short range data units, by a factor of N,to a lower clock rate to be used for transmitting long range data units.The down-clocking factor N is different in different embodiments and/orscenarios. For example, in one embodiment and/or scenario, down-clockingfactor N is equal to 10. In this embodiment, a long range data unitgenerated using the down-clocked clock rate is transmitted over a timethat is ten times longer than the time it takes to transmit thecorresponding short range data unit. In the frequency domain, accordingto this embodiment, a long range data unit generated using thedown-clocked clock rate occupies a bandwidth that is ten times smallerthan the bandwidth occupied by the corresponding short range data unit.In other embodiments and/or scenarios, other suitable down-clockingfactor (N) values are utilized, and transmission times and bandwidths oflong range data units are scaled accordingly. In some embodiments and/orscenarios, the down-clocking factor N is a power of two (e.g., N=8, 16,32, etc.). In some embodiments, the long range communication protocolspecifies more than one down-clocking factor N, with a differentdown-clocking factor N used in a different geographical region (e.g.,N=16 in US, N=64 in Europe) to accommodate different bandwidthrequirements of the different regions, for example. Some examples ofdata unit formats defined by a long range communication protocol,according to some embodiments, are described in U.S. patent applicationSer. No. 13/359,336, filed on Jan. 26, 2012, which is herebyincorporated by reference herein in its entirety.

According to an embodiment, in order to perform beamforming, abeamformer (e.g., the network interface 16 of the AP 14) generates andtransmits a sounding packet (e.g., an NDP sounding packet), whichincludes one or more known training signals, to a beamformee (e.g. theclient station 25-1), and the beamformee determines (e.g., the networkinterface 27 of the client station 25-1 determines), based on thereceived training signals, CSI of the communication channel between thebeamformee and the beamformer. In one implementation, the beamformeethen transmits (e.g., the network interface 27 of the client station25-1 transmits) the CSI back to the beamformer, which then generates(e.g., the network interface 16 of the AP 14 generates) the beamformingmatrix using the CSI. In another implementation, the beamformee uses theCSI to generate the beamforming matrix, and then transmits coefficientsof the beamforming matrix back to the beamformer. In variousembodiments, NDP sounding packet format specified by the long rangecommunication protocol is based on an single user (SU) PHY preambleformat specified by a short range communication protocol (e.g., preambleof the data unit 200 of FIG. 2A, preamble of the data unit 300 of FIG.3, preamble of the data unit 400 of FIG. 4, preamble of the data unit500 of FIG. 5, or another preamble specified by a short rangecommunication protocol, or another suitable short range preamble)generated using a lower clock rate compared to the clock rate used togenerate PHY data units that conform to the short range communicationprotocol.

FIG. 8A is a diagram of an NDP sounding packet 800 that the networkinterface 16 of the AP 14 is configured to generate and to transmit tothe client station 25-1 via orthogonal frequency domain multiplexing(OFDM) modulation when operating in a long range mode, according to anembodiment. In an embodiment, the NDP sounding packet 800 includes a PHYpreamble formatted the same as the greenfield preamble 401 of the dataunit 400 (FIG. 4) except that the NDP sounding packet 800 is transmittedusing a clock rate that is down-clocked from the short range clock rateby a down-clocking factor N. As a result, each OFDM symbol of the NDPpacket 800 is N times longer in time duration compared to an OFDM symbolincluded in the preamble 401 of the data unit 400. In the embodiment ofFIG. 8A, N is equal to 10. Accordingly, each OFDM symbol included in theNDP sounding packet 800 is 10 times longer compared to an OFDM symbolincluded in the preamble portion 401 of the data unit 400. Accordingly,in the NDP sounding packet 800, each OFDM symbol of the NDP sounding is40 μs in duration. As illustrated in FIG. 8A, the NDP sounding packet800 includes a two-OFDM symbol (80 μs) GF-STF field 802, a two-OFDMsymbol (80 μs) LTF1 field 804, a two-OFDM symbol (80 μs) SIG field 806,and M one-OFDM symbol LTF fields 808. In other embodiments, othersuitable down-clocking factors are utilized, resulting in OFDM symbolduration different from the OFDM symbol duration of the NDP soundingpacket 800. The NDP sounding packet 800 omits a data payload portion.

In order to allow the client station 25-1 to obtain a full channelestimate of the communication channel, in various embodiments and/orscenarios, the number of long training fields included in the NDPsounding packet 800 equals the number of transmit antennas 24 of AP 14.As an example, FIG. 8B is an example NDP sounding packet 850 generatedand transmitted by network interface 16 of the AP 14 in a case in whichthe AP 14 includes four antennas 24. Accordingly, as illustrated in FIG.8B, the NDP sounding packet 850 includes four LTF fields 858.

FIG. 9 is a diagram of an NDP sounding packet 900 that the networkinterface 16 of the AP 14 is configured to generate and to transmit tothe client station 25-1 via orthogonal frequency domain multiplexing(OFDM) modulation when operating in a long range mode, according to anembodiment. The NDP sounding packet 900 includes only a preamble that isformatted similar to the mixed preamble portion 501 of the data unit 500of FIG. 5, except that the NDP sounding packet 900 is transmitted usinga clock rate that is down-clocked from the short range clock rate by adown-clocking factor N. As a result, symbol duration of each OFDM symbolof the NDP packet 900 is N times longer compared to symbol duration ofan OFDM symbol included in the preamble portion 501 of the data unit500. In the embodiment of FIG. 8, N is equal to 10. Accordingly, eachOFDM symbol included in the NDP sounding packet 900 is 10 times longercompared to an OFDM symbol included in the preamble portion 401. Inparticular, in the embodiment of FIG. 9, each OFDM symbol of the NDPsounding is 40 μs in duration. As illustrated, in this embodiment, theNDP sounding packet 900 includes a two-OFDM symbol (80 μs) L-LTF field902, a two-OFDM symbol (80 μs) L-LTF field 904, a one-OFDM symbol (40μs) L-SIG field 906, a two-OFDM symbol (80 μs) HT-SIG field, a two-OFDMsymbol (80 μs) HT-SIG field 906, a one-OFDM symbol (40 μs) HT-STF field910, and M one-OFDM symbol LTF fields 912. In order to allow the clientstation 25-1 to obtain a full channel estimate of the communicationchannel, in various embodiments and/or scenarios, the number of longtraining fields included in a sounding packet equals the number oftransmitting antennas at the transmitter (e.g., AP 14). Thus, in anembodiment, the number M of the LTF fields 912 equals the number oftransmit (or transmit/receive) antennas 24 of the AP 14. The NDPsounding packet 900 omits a data payload portion.

FIG. 10 is a diagram of an NDP sounding packet 1000 that the networkinterface 16 of the AP 14 is configured to generate and to transmit tothe client station 25-1 via orthogonal frequency domain multiplexing(OFDM) modulation when operating in a long range mode, according to anembodiment. The NDP sounding packet 1000 is similar to the NDP soundingpacket 900 of FIG. 9 except that that the legacy portion of the preamble(i.e., L-STF 902, L-LTF 904, L-SIG 906) is omitted from the data unit1000. Further, in the NDP sounding packet 1000, the STF field 1002 andthe first LTF field (VHT-LTF1 field 1004-1) precede the VHT-SIG-A field1006, and the remaining VHT-LTF fields 1004 follow the VHT-SIG-A field1006. Additionally, the VHT-STF field 1002 is longer than the HT-STFfield 910. In one embodiment, to shorten the NDP sounding packet 1000,the VHT-SIG-B field (generally used for information needed for decodingmulti user data units) 1010 is omitted from the NDP sounding packet1000. The NDP sounding packet 1000 omits a data payload portion.

In some embodiments, in addition to the down-clocked modes of operationdiscussed above (“normal PHY modes”), the long range communicationprotocol also specifies one or more “extended range modes” with areduced data rate compared to the lowest data rate of the normal modesand/or occupying a smaller bandwidth (e.g., generated using a smallersize Fast Fourier Transform (FFT)) compared to the lowest bandwidthspecified for normal modes PHY mode. Because of the lower data rate, theextended range mode further extends communication range and generallyimproves receiver sensitivity. In some such embodiments, PHY preambleformat specified by the long range communication protocol for theextended range mode (“extended range mode preamble”) is differentcompared to the PHY preamble format specified for normal mode (“normalmode preamble”). Accordingly, in at least some such embodiments, NDPsounding packets used in the extended range mode (“extended range modeNDP sounding packets”) are formatted differently compared to NDPsounding packets used in normal mode (“normal mode NDP soundingpackets”). For instance, an extended range mode NDP sounding packetincludes a longer long training sequence for better channel estimationand/or a longer short training sequence for better packet detection andsynchronization at a receiving device, in some embodiments. In someembodiments, PHY preamble format specified by the long range protocolfor extended range mode includes an extra preamble portion in additionto the preamble specified for the normal mode. Some examples of preambleformats defined by the long range communication protocol for theextended range mode that correspond to NDP sounding packet formatsaccording to some embodiments are described in U.S. patent applicationSer. No. 13/359,336, filed on Jan. 26, 2012, which is herebyincorporated by reference herein in its entirety.

FIG. 11 is a diagram of an example NDP sounding packet 1100 used in theextended range mode, according to an embodiment. The NDP sounding packet1100 is similar to the normal mode NDP sounding packet 800 of FIG. 8Aexcept that the NDP sounding packet 1100 includes an STF field 1102 thatis longer compared to the STF field 802 of the NDP sounding packet 800.The longer STF field 1102 includes more repetitions of a trainingsequence compared to the number of repetitions included in the STF field802 of the normal PHY mode NDP sounding packet 800. As an example, thelonger STF field 1102 includes four OFDM symbols and, accordingly, is160 μs long compared to an 80 μs duration of the STF field 802. Inanother embodiment, the STF field 1102 is of a different durationgreater than the 80 μs duration of the STF field 802. The soundingpacket 1100 also includes a signal field 1106 that is longer compared tothe signal field 806 of the sounding packet 800. Further, in someembodiments, each long training field 1104 included in the soundingpacket 1100 is the same in duration as each corresponding long trainingfield 804 of the sounding packet 800. In another embodiment, one or moreof the long training fields 1104 of the sounding packet 1100 is longercompared to the corresponding long training field 804 of the soundingpacket 800. The NDP sounding packet 1100 omits a data payload portion.

In some embodiments, the long range communication protocol specifies asingle stream format for extended range mode regular data units. Thatis, in such embodiments, data units in the extended range mode aregenerally transmitted using only one spatial stream. Accordingly, insuch embodiments, the extended range preamble format defined by the longrange communication protocol includes only one long training fieldallowing a receiving device to generate a measurement of a singledimension communication channel. In such embodiments, if the AP 14and/or the client station being sounded includes more than one antenna,a sounding packet needs to include multiple long training fields toallow the client station to obtain a full dimensional measurement of thecommunication channel. To this end, according to an embodiment, the longrange communication protocol specifies a multi-stream NDP soundingpacket format to be used in the extended range mode, even thoughextended range mode data packets are transmitted in a single streamformat using only one spatial stream. In such embodiment, extended rangeNDP sounding packets include additional long training fields in additionto the single long training field specified for the extended rangepreamble format for regular data units transmitted in the extended rangemode.

According to an embodiment, multiple long training fields included in anNDP sounding packet (for normal and/or extended mode) are spread overthe multiple spatial or space-time streams by a mapping matrix P. In oneembodiment, the number of LTFs included in an NDP sounding packetdepends on the number of antennas included in the AP. For example,according, to an embodiment, if the AP 14 includes two antennas, thenthe number of LTF fields included in each sounding packet that the AP 14transmits is two. In the same embodiment, if the AP 14 includes eitherthree or four antennas, then the number of LTF fields included in eachsounding packet that the AP transmits is four. In general, in variousembodiments, the number of LTFs included in a sounding packettransmitted by the AP 14 is any suitable number greater or equal to thenumber of antennas at the AP 14. In any case, in an embodiment, the LTFsincluded in a sounding (e.g. in the sounding packet 800 of FIG. 8A, thesounding packet 1100 of FIG. 11, etc.) are mapped to the multiplespatial or space-time streams according to:[HTLTF1_(k),HTLTF2_(k), . . . ,HTLTFN_(k) ]=Q _(k) D _(CSD) ^((k)) A_(HTLTF)LTF_(k)  Equation 1where the subscript k denotes a tone index, Q is a spatial mappingmatrix, D_(CSD) is a diagonal matrix with diagonal elements representingcyclic shifts in the time domain, A_(HTLTF) is a mapping matrix for thelong training field, and LTF_(k) is the long training field value forthe k^(th) tone.

As an example, the mapping matrix P used to map LTF tones in an NDPsounding packet to multiple spatial or space-time streams, in oneembodiment, is given by:

$\begin{matrix}{P_{HTLTF} = \begin{bmatrix}1 & {- 1} & 1 & 1 \\1 & 1 & {- 1} & 1 \\1 & 1 & 1 & {- 1} \\{- 1} & 1 & 1 & 1\end{bmatrix}} & {{Equation}\mspace{14mu} 2}\end{matrix}$

In an embodiment, a submatrix of the mapping matrix in Equation 2 isused for mapping LTF tones if the sounding packet is to be transmittedusing less than four spatial or space-time streams (e.g., a 2×2submatrix for two spatial or space-time streams with two LTFs, a 3×4submatrix for three spatial or space-time streams with four LTFs, etc.).

In some embodiments, one or more of the long training fields included inan NDP sounding packet include pilot tones to allow a receiving deviceto accurately track frequency and/or phase offsets caused by thecommunication channel between the AP and the client station. Longertransmission channels over which long range NDP sounding packetstypically travel result in a larger frequency and phase offsets betweena transmitter and a receiver compared to frequency and/or phase offsetsexperienced by similar short range NDP packets, in at least somesituations. Accordingly, in an embodiment, to combat the largerfrequency offset, NDP sounding packets include single stream pilot tonesin some or all of the long training fields. For clarity, single streampilot tone insertion techniques are explained below with reference tothe NDP sounding packet 850 of FIG. 8B. However, these or similar pilotinsertion techniques are applied to other NDP sounding packet formats(e.g., sounding packets of FIG. 8B, FIG. 9. FIG. 10. FIG. 11, etc.), orother suitable NDP sounding packet formats, according to otherembodiments.

With reference to FIG. 4, the short range data unit 400 does not includepilot tones in any of the HT-LTF fields 408. Referring to FIG. 8A, theNDP sounding packet 800 is generated for long range transmission and,accordingly, includes OFDM symbols of longer duration and, consequently,LTF fields of the sounding packet 800 are longer compared to the LTFfields of the data unit 400. As a result, a long training field istypically subject to a greater phase shift during transmission in longrange mode than in short range mode. To mitigate the phase shiftproblem, in some embodiments, pilot tones are inserted into at leastsome of the training fields of the long range NDP sounding packet 800and are used for phase tracking between the transmitter and thereceiver. According to an embodiment, the NDP sounding packet 800 is amulti-stream sounding packet transmitted over a number of spatialstreams in at least some situations. In this embodiment, if the insertedpilot tones are also multi-stream (e.g., mapped to the multiple spatialor space-time streams using the same mapping matrix as the mappingmatrix used to map data tones), then at least a corresponding number oflong training fields needs to be received before phase tracking can beperformed. To enable a receiving device to perform phase tracking priorto having received all long training fields, in some embodiments, thepilot tones included in one or more of the long training fields 804 ofthe data unit 800 are single-stream pilot tones.

With continued reference to FIG. 8A, in an embodiment, the OFDM data andpilot tones of the HT-LTF fields 804 are mapped to multiple spatial orspace-time streams according to:

$\begin{matrix}{{\left\lbrack {{{HTLTF}\; 1_{k}},{{HTLTF}\; 2_{k}},\ldots\mspace{14mu},{HTLTFN}_{k}} \right\rbrack = {Q_{k}D_{CSD}^{(k)}A_{HTLTF}^{k}{LTF}_{k}}}\mspace{79mu}{A_{HTLTF}^{k} = \left\{ \begin{matrix}{R_{HTLTF},} & {{{if}\mspace{14mu} k} \in K_{Pilot}} \\{P_{HTLTF},} & {otherwise}\end{matrix} \right.}} & {{Equation}\mspace{14mu} 3}\end{matrix}$where the subscript k denotes a tone index, Q is a spatial mappingmatrix, D_(CSD) is a diagonal matrix with diagonal elements representingcyclic shifts in the time domain, A_(HTLTF) is a mapping matrix for thelong training field, and LTF_(k) is the long training field value forthe k^(th) tone. With continued reference to Equation 3, K_(pilot)represents a set tone indices corresponding to pilot tones, andP_(HTLHF) is a mapping matrix used for mapping long training field datatones to multiple spatial streams. As an example, according to anembodiment, P_(HTLHF) for mapping LTF non-pilot tones to spatial orspace-time streams is given by Equation 2 (above). Further, theR_(HTLFT) matrix is a mapping matrix for LTF pilot tones, which isdefined differently in different embodiments. In one embodiment, theR_(HTLFT) matrix is given by:[R _(HTLTF)]_(m,n) =[P _(HTLTF)]_(m,1),1≦m,n≦N _(HTLTF)  Equation 3.

Accordingly, in this embodiment, all pilot tones in HT-LTF fields 804are mapped to multiple spatial or space-time streams using the firstcolumn of the spatial stream mapping matrix P.

In another embodiment, the R_(HTLFT) matrix is as defined in the IEEE802.11ac Standard, given by:[R _(HTLTF)]_(m,n) =[P _(HTLTF)]_(l,m), 1≦m,n≦N _(HTLTF)  Equation 4.Accordingly, in this embodiment, all pilot tones in HT-LTF fields 804are mapped to multiple spatial or space-time streams using the first rowof the spatial stream mapping matrix P.

According to an embodiment, the AP 14 signals to a client station the apacket is an NDP sounding packet rather than a regular data unit usingan indication included in a signal field of the NDP sounding packet or asignal field included in a preamble of a regular data unit. For example,in an embodiment, a length or a duration subfield included in the signalfield is set to a value of zero to indicate that the packet is asounding packet, and is used to indicate a length of the packet in thecase of a regular data unit. In another embodiment, the long rangecommunication protocol specifies signal field bit allocation thatincludes a bit to specifically indicate whether the packet is an NDPsounding packet or a regular data unit. In yet another embodiment, thelong range communication protocol specifies a value for a subfield ofthe signal field typically not used for regular data units (i.e., avalue outside of possible values specified for regular data units by thelong range communication protocol) to be used to signal a soundingpacket. As an example, in some embodiments, the long range communicationprotocol specifies a valid range of values between 0 and 10 a signalfield subfield used to specify the modulation and coding scheme (MCS)used to transmit the data unit. In one such embodiment, the long rangecommunication protocol specifies that a value in the MCS subfield otherthan a value in the valid MCS values range specified for regular dataunits indicates that the data unit is a sounding packet (e.g., a valueof 11, 12, 13, etc.). In some such embodiments, the length subfield of asignal field can be used to communicate information other than thelength of the packet (e.g., to communicate the number of spatial orspace time streams for which the NDP sounding packet is generated). Insome embodiments, a sounding packet is identified by more than onesubfields of the signal field. For example, in one embodiment, a signalfield of an NDP sounding packet includes an MCS subfield with an MCSvalue that is a suitable value other than a valid value specified forregular data units and also includes a value of zero in the length orduration subfield.

In some embodiments in which the extended range mode PHY preamble formatis specified for only a single spatial stream, the preamble format neednot include an indication of the number of spatial streams correspondingto the regular extended range data units. On the other hand, asdiscussed above, NDP sounding packets are multi-stream packets thatallow a receiver to estimate a full dimensional response of thecommunication channel even in an extended range mode in which regulardata unit are always single stream packets. Accordingly, in variousembodiments, an indication of the number of spatial or space-timestreams of an extended range NDP sounding packet is signaled in thesignal field of the NDP sounding packet.

FIG. 12A is a diagram of an example signal field 1200 included in an NDPsounding packet and/or in a preamble of a regular data unit, accordingto an embodiment. In an embodiment, the signal field 1200 is alsoincluded in a preamble portion of a regular data unit transmitted innormal and/or in extended range mode. The signal field 1200 includes aLength subfield 1202, a number of spatial or space-time streams (Nsts)subfield 1204, a Reserved subfield 1206, a cyclic redundancy check(CRC)/Parity check subfield 1208 and a Tail subfield 1210. In anembodiment, a first value (e.g., zero) in the Length subfield 1202indicates to a receiver that the packet is an NDP sounding packet ratherthan a regular data unit. In this case, in an embodiment, the Nstssubfield 1204 is used to indicate the number of spatial or space-timestreams corresponding to the NDP sounding packet 800. On the other hand,the Length subfield 1202 is not set to the first value (e.g., the Lengthsubfield 1202 is non-zero) (i.e., the signal field 1200 belongs to aregular data unit rather than an NDP sounding packet), then the Nstssubfield 1204 is interpreted as a reserved subfield.

FIG. 12B is a diagram of an example signal field 1230 included in an NDPsounding packet and/or in a preamble of a regular data unit, accordingto an embodiment. In an embodiment, the signal field 1230 is alsoincluded in a preamble portion of a regular data unit transmitted innormal and/or in extended range mode. The signal field 1230 includes anNDP field 1232, a Length/Nsts subfield 1234, a Reserved subfield 1236, acyclic redundancy check (CRC)/Parity check subfield 1238 and a Tailsubfield 1240. In an embodiment, the NDP subfield 1232 is set to a firstvalue (e.g., a logic one (1)) to indicate that the packet is an NDPsounding packet and to a second value (e.g., a logic zero (0)) toindicate that the packet is a regular data unit. In an embodiment, theNDP subfield 1232 is replaced by a regular subfield specified for aregular data unit. In this case, to indicate that the packet is asounding packet, the regular subfield is set to a value different than avalid value used for regular data units, according to an embodiment. Forexample, in one embodiment, the NDP subfield 1232 is replaced by an MCSsubfield generally used to signal a modulation and coding scheme usedfor transmitting the regular data unit. In this embodiment, the subfieldspecified for the regular data unit is set to a value other than a validMCS value specified as a suitable MCS value for regular data units. Forexample, in an embodiment in which a valid MCS value specified forregular data units is a value in the range of 0 through 10, the MCSsubfield is set to a value other than a value in the range of 0 through10 (e.g. 11, 12, 13, etc.) to indicate that the packet is a soundingpacket and not a regular data unit. If the NDP subfield (or anothersubfield, such as an MCS subfield) indicates that the packet is asounding packet, a suitable number of bits of the Length subfield 1234are used to indicate the number of spatial or space-time streams of theNDP sounding packet. For example, in an embodiment, the first two bitsof the Length subfield 1234 are used to indicate up to four spatial orspace-time streams. According to an embodiment, unused bits of theLength subfield 1234 are set to a value of zero, for example. On theother hand, if the packet is a regular data unit rather than NDPsounding packet, as indicated by the NDP subfield 1232, then theLength/Nsts subfield 1234 is used to signal the length of the data unitto the receiving device.

FIG. 12C is a diagram of an example signal field 1250 included in an NDPsounding packet and/or in a preamble of a regular data unit, accordingto an embodiment. In an embodiment, the signal field 1250 is alsoincluded in a preamble portion of a regular single stream data unittransmitted in extended range mode. The signal field 1250 includes aLength subfield 1262, a Scrambler seed/Nsts subfield 1264, a Reservedsubfield 1266, a cyclic redundancy check (CRC)/Parity check subfield1268, and a Tail subfield 1270. In an embodiment, the Scramblerseed/Nsts subfield 1264 is implemented using four bits. In anembodiment, a first value (e.g., zero) in the Length subfield 1202indicates to a receiver that the packet is an NDP sounding packet ratherthan a regular data unit. In this case, a suitable number of bits of theScramble seed/Nsts subfield 1264 are used to indicate the number ofspatial or space-time streams included in the NDP sounding packet. Forexample, in one embodiment, two bits (e.g., two least significant bits(LSB)) of the Scrambler seed/Nsts subfield 1264 are used to indicate thenumber of spatial or space-time streams. In this case, according to anembodiment, bits of the Scrambler seed/Nsts subfield 1264 not being usedto indicate the number of spatial or space-time streams are reserved.For example, in an embodiment, two most significant bits (MSB) of theScrambler seed/Nsts subfield 1264 are reserved.

In an embodiment, a value not equal to the first value (e.g., a valuegreater than zero) in the Length field 1262 indicates that the packet isa regular data unit. In this case, the Scrambler seed/Nsts subfield 1264is used to indicate a value of the scrambler seed needed to properlyprocess the data payload portion of the data unit (or a portion of thescrambler seed if the scrambler seed value includes more bits comparedto the number of bits allocated for Scrambler seed/Nsts subfield 1264).For example, in an embodiment, if four bits are allocated for theScrambler seed/Nsts subfield 1264, then four LSB of the scrambler seedare represented by the Scrambler seed/Nsts subfield 1264. In anembodiment, the scrambler seed is seven bits long. In this embodiment,each of the remaining three bits (3 MSB) of the scrambler seed is fixedto logic one (1). In this embodiment, because the signal field 1260includes a field an indicating the scrambler seed for processing dataunits, a service field (which is typically used to signal the value ofthe scrambler seed) is omitted from the corresponding data unit.

In various embodiments, the network interface 16 of the AP 14 isconfigured to generate NDP packets and regular packets that includesignal fields according to one or more of the formats in FIGS. 12A, 12B,12C. In various embodiments, the network interface 27 of the clientdevice 25-1 is configured to generate NDP packets and regular packetsthat include signal fields according to one or more of the formats inFIGS. 12A, 12B, 12C.

In various embodiments, upon receiving a packet including a signal field1200, 1230, or 1260, the network interface 16 of the AP 14 is configuredto interpret one or more of the subfields 1204, 1234, 1264,respectively, differently depending on the values of the subfields 1202,1232, and 1262, respectively, as discussed above. In variousembodiments, upon receiving a packet including a signal field 1200,1230, or 1260, the network interface 27 of the client station 25-1 isconfigured to interpret one or more of the subfields 1204, 1234, 1264,respectively, differently depending on the values of the subfields 1202,1232, and 1262, respectively, as discussed above.

In some embodiments, the AP 14 and/or the client station 25-1 is able tooperate in dual band configurations. In such embodiments, the AP 14 isable to switch between short range and long range modes of operation.Accordingly, in an embodiment, when operating in a short range mode, theAP 14 transmits and receives data units that conform to one or more ofthe short range communication protocols, and when operating in a longrange mode, the AP 14 transmits and receives data units that conform tothe long range communication protocol. In an embodiment, a dual banddevice utilizes a first clock suitable for short range operation andutilizes a second clock suitable for long range operation, where afrequency of the second clock is lower than a frequency of the firstclock by a factor of N. In an embodiment, a dual band device generatesthe second clock signal for long range operation by down-clocking thefirst clock signal by a factor N. Accordingly, in such embodiments, theclock rate used in long range mode is a fraction of a clock rate used inshort range mode. In such embodiments, NDP sounding packets for longrange are generated according to a short range preamble format specifiedby a short range communication protocol but using the lower clock rate,as discussed above. Further, in some embodiments, the AP 14 and/or theclient station 25-1 is a dual band device that is able to switch betweendifferent low frequency bands defined for long range operation by thelong range communication protocol (e.g., different sub-1 GHz frequencyband defined by the long range communication protocol for differentgeographical areas). In yet another embodiment, the AP 14 and/or theclient station 25-1 is a single band device configured to operate inonly one long range frequency band and to generate NDP sounding packetsbased on preamble format (or formats) specified by the long rangecommunication protocol.

FIG. 13 is a flow diagram of an example method 1300 for generating anNDP sounding packet, according to an embodiment. With reference to FIG.1, the method 1300 is implemented by the network interface 16 of the AP14, in an embodiment. For example, in one such embodiment, the PHYprocessing unit 20 is configured to implement the method 1300. Accordingto another embodiment, the MAC processing 18 is also configured toimplement at least a part of the method 1300. With continued referenceto FIG. 1, in yet another embodiment, the method 1300 is implemented bythe network interface 27 (e.g., the PHY processing unit 29 and/or theMAC processing unit 28) of the client station 25-1. In otherembodiments, the method 1300 is implemented by other suitable networkinterfaces.

At block 1302, a signal field to be included in the NDP sounding packetis generated. For example, in one embodiment, the signal field 806 ofFIG. 8A is generated. In another embodiment, one of signal fields 1200of FIG. 12A, signal field 1230 of FIG. 12B or the signal field 1260 ofFIG. 12C is generated. In another embodiment, another suitable signalfield is generated.

At block 1304, one or more long training fields are generated. In anembodiment, the number of training fields generated at block 1304 isgreater than or equal to the number of antennas included in thetransmitting device. At block 1306, the signal field generated at block1302 and the one or more long training fields generated at block 1304are modulated using OFDM modulation. The symbol duration of each OFDMsymbol generated at block 1306 is at least 8 μs, in an embodiment. Inone embodiment, the OFDM symbol duration is 40 μs. In anotherembodiment, the OFDM symbol duration is another suitable value of atleast 8 μs. At block 1308, the NDP sounding packet is generated toinclude the OFDM symbols generated at block 1306.

FIG. 14 is a flow diagram of an example method 1400, according to anembodiment. With reference to FIG. 1, the method 1400 is implemented bythe network interface 16 of the AP 14, in an embodiment. For example, inone such embodiment, the PHY processing unit 20 is configured toimplement the method 1400. According to another embodiment, the MACprocessing 18 is also configured to implement at least a part of themethod 1400. With continued reference to FIG. 1, in yet anotherembodiment, the method 1400 is implemented by the network interface 27(e.g., the PHY processing unit 29 and/or the MAC processing unit 28) ofthe client station 25-1. In other embodiments, the method 1400 isimplemented by other suitable network interfaces.

At block 1402, it is determined in which mode the NDP sounding packet isto be transmitted. If it is determined at block 1402 that the NDPsounding packet is to be transmitted in a normal PHY mode, then the NDPsounding packet is generated according to a first NDP sounding packetformat at block 1404. In an embodiment, the NDP sounding packet isgenerated according to the format illustrated in FIG. 8A. In anotherembodiment, the NDP sounding packet is generated at block 1404 accordingto another suitable NDP sounding packet format. On the other hand, if itis determined at block 1402 that the NDP sounding packet is not to betransmitted in a normal PHY mode (i.e., the NDP sounding packet is to betransmitted in an extended range mode), then the NDP sounding packet isgenerated according to a second PHY sounding packet format at block1406. In an embodiment, the NDP sounding packet at block 1406 isgenerated according to the PHY sounding packet format of FIG. 11. Inanother embodiment, the NDP sounding packet at block 1406 is generatedaccording to another suitable PHY sounding packet format different formthe first sounding data packet format used at block 1404.

At least some of the various blocks, operations, and techniquesdescribed above may be implemented utilizing hardware, a processorexecuting firmware instructions, a processor executing softwareinstructions, or any combination thereof. Also, some of the variousblocks, operations, and techniques may be performed in a different order(and/or concurrently) and still achieve desirable results. Whenimplemented utilizing a processor executing software or firmwareinstructions, the software or firmware instructions may be stored in anycomputer readable memory such as on a magnetic disk, an optical disk, orother storage medium, in a RAM or ROM or flash memory, processor, harddisk drive, optical disk drive, tape drive, etc. Likewise, the softwareor firmware instructions may be delivered to a user or a system via anyknown or desired delivery method including, for example, on a computerreadable disk or other transportable computer storage mechanism or viacommunication media. Communication media typically embodies computerreadable instructions, data structures, program modules or other data ina modulated data signal such as a carrier wave or other transportmechanism. The term “modulated data signal” means a signal that has oneor more of its characteristics set or changed in such a manner as toencode information in the signal. By way of example, and not limitation,communication media includes wired media such as a wired network ordirect-wired connection, and wireless media such as acoustic, radiofrequency, infrared and other wireless media. Thus, the software orfirmware instructions may be delivered to a user or a system via acommunication channel such as a telephone line, a DSL line, a cabletelevision line, a fiber optics line, a wireless communication channel,the Internet, etc. (which are viewed as being the same as orinterchangeable with providing such software via a transportable storagemedium). The software or firmware instructions may include machinereadable instructions that, when executed by the processor, cause theprocessor to perform various acts.

When implemented in hardware, the hardware may comprise one or more ofdiscrete components, an integrated circuit, an application-specificintegrated circuit (ASIC), etc.

While the present invention has been described with reference tospecific examples, which are intended to be illustrative only and not tobe limiting of the invention, changes, additions and/or deletions may bemade to the disclosed embodiments without departing from the scope ofthe invention.

What is claimed is:
 1. A method for generating a null data packet (NDP)sounding packet for transmission via a communication channel, the methodcomprising: generating a signal field, wherein generating the signalfield comprises including in the signal field a sub-field that indicatesa number of spatial or space-time streams corresponding to the NDPsounding packet, wherein the sub-field corresponds to a portion of thesignal field that, when included in regular packets that are not NDPsounding packets, is used for a purpose other than indicating a numberof spatial or space-time streams; generating one or more long trainingfields; modulating the signal field and the long training fields using aplurality of orthogonal frequency division multiplexing (OFDM) symbols,wherein symbol duration of each OFDM symbol of the plurality of OFDMsymbols is at least 8 μs; and generating the NDP sounding packet toinclude the plurality of OFDM symbols, wherein the NDP sounding packetomits a data payload portion.
 2. A method according to claim 1, whereingenerating the one or more long training fields includes generating atleast one of the one or more training fields to include pilot tones andnon-pilot tones; wherein the method further comprises: mapping thenon-pilot tones to a plurality of multiple spatial or space-time streamsusing a mapping matrix; and mapping the pilot tones to the plurality ofmultiple spatial or space-time streams using a column of the mappingmatrix.
 3. A method according to claim 2, wherein the column of themapping matrix used to map pilot tones to the multiple spatial orspace-time streams is the first column of the mapping matrix.
 4. Amethod according to claim 1, wherein generating the one or more longtraining fields includes generating at least one of the one or moretraining fields to include pilot tones and non-pilot tones; wherein themethod further comprises: mapping the non-pilot tones to a plurality ofmultiple spatial or space-time streams using a mapping matrix; andmapping the pilot tones to the plurality of multiple spatial orspace-time streams using a row of the mapping matrix.
 5. A methodaccording to claim 4, wherein the row of the mapping matrix used to mappilot tones to the multiple spatial or space-time streams is the firstrow of the mapping matrix.
 6. A method according to claim 1, wherein theNDP sounding packet is formatted according to a PHY preamble format of aregular packet; wherein the method further comprises setting each of oneor more subfields in the signal field to a respective first value tosignal to a receiving device that the NDP sounding packet is a soundingpacket and not a regular data unit.
 7. A method according to claim 6,wherein the one or more subfields include at least one of i) a lengthsubfield and ii) a modulation and coding scheme (MCS) subfield.
 8. Amethod according to claim 7, further comprising setting the lengthsubfield to a value of zero to signal to the receiving device that theNDP sounding packet is a sounding packet.
 9. A method according to claim7, further comprising setting the MCS subfield to a value other than avalid MCS value to signal to the receiving device that the NDP soundingpacket is a sounding packet, wherein the valid MCS value is a value usedto indicate an MCS for a regular data unit.
 10. An apparatus comprising:a network interface configured to generate a signal field, whereingenerating the signal field comprises including in the signal field asub-field that indicates a number of spatial or space-time streamscorresponding to the NDP sounding packet, wherein the sub-fieldcorresponds to a portion of the signal field that, when included inregular packets that are not NDP sounding packets, is used for a purposeother than indicating a number of spatial or space-time streams,generate one or more long training fields, modulate the preamble portionusing a plurality of orthogonal frequency division multiplexing (OFDM)symbols, wherein symbol duration of each OFDM symbol of the plurality ofOFDM symbols is at least 8 μs, and generate the NDP sounding packet toinclude the plurality of OFDM symbols, wherein the NDP sounding packetdoes omits a data payload portion.
 11. An apparatus according to claim10, wherein the network interface is configured to: generate at leastone of the one or more training fields to include pilot tones andnon-pilot tones; map the non-pilot tones to multiple spatial orspace-time streams using a mapping matrix; and map the pilot tones tomultiple spatial or space-time stream a column of the mapping matrix.12. An apparatus according to claim 11, wherein the network interface isconfigured to map pilot tones to multiple spatial or space-time streamsusing the first column of the mapping matrix.
 13. An apparatus accordingto claim 10, wherein the network interface is configured to: generate atleast one of the one or more training fields to include pilot tones andnon-pilot tones; map the non-pilot tones to multiple spatial orspace-time streams using a mapping matrix; and map the pilot tones tomultiple spatial or space-time stream a row of the mapping matrix. 14.An apparatus according to claim 13, wherein the network interface isconfigured to map pilot tones to multiple spatial or space-time streamsusing the first row of the mapping matrix.
 15. An apparatus according toclaim 10, wherein the NDP sounding packet is formatted according to aPHY preamble format of a regular packet; wherein the network interfaceis further configured to set each of one or more subfields in the signalfield to a respective first value to signal to a receiving device thatthe NDP sounding packet is a sounding packet and not a regular dataunit.
 16. An apparatus according to claim 15, wherein the one or moresubfields include at least one of i) a length subfield and ii) amodulation and coding scheme (MCS) subfield.
 17. An apparatus accordingto claim 16, wherein the network interface is configured to set thelength subfield to a value of zero to signal to the receiving devicethat the NDP sounding packet is a sounding packet.
 18. An apparatusaccording to claim 16, wherein the network interface is configured toset the MCS subfield to a value other than a valid MCS value to signalto the receiving device that the NDP sounding packet is a soundingpacket, wherein the valid MCS value is a value used to indicate an MCSfor a regular data unit.
 19. A method comprising: generating a regulardata unit that includes a data payload portion, wherein the data unit isto be transmitted in an extended range physical layer (PHY) mode;generating a signal field including generating a first subfield and asecond subfield, wherein the signal field is to be included in one of i)a preamble of the regular data unit or ii) a first null data packet(NDP) to be transmitted in the extended range mode; generating a secondNDP sounding packet according to a first PHY sounding packet formatspecified by a communication protocol, wherein the second NDP soundingpacket is to be transmitted in a normal PHY mode; and generating thefirst NDP sounding packet according to a second PHY sounding packetformat defined by the communication protocol, wherein the NDP soundingpacket is to be transmitted in the extended range PHY mode.
 20. A methodaccording to clam 19, wherein the first PHY sounding packet format isbased on a first PHY preamble format specified by the communicationprotocol to be included in data units transmitted in the normal PHYmode, and wherein the second PHY sounding packet format is based on asecond PHY preamble format specified by the communication protocol to beincluded in data units transmitted in the extended range PHY mode.
 21. Amethod according to claim 20, wherein the second PHY preamble format isspecified for single stream data units and wherein the second PHYsounding packet format is specified for multi stream sounding packets.22. A method according to claim 19, wherein: the first subfield is alength subfield i) set to a value other than a first value when thesignal field is to be included in the regular data unit and ii) set tothe first value when the signal field is to be included in the first NDPsounding packet; and the second subfield includes a number of streamsindicator when signal field is to be included in the first NDP soundingpacket.
 23. A method according to claim 19, wherein: the first subfieldis a length subfield i) set to a value other than a first value when thesignal field is to be included in the regular data unit and ii) set tothe first value when the signal field is to be included in the first NDPsounding packet; and the second subfield includes i) a number of streamsindicator when the signal field is to be included in the first NDPsounding packet and ii) a scrambler seed value when the signal field isto be included in the regular data unit.
 24. A method according to claim19, wherein: the first subfield is used to indicate whether the packetis the regular data unit or the first NDP sounding packet; and thesecond subfield includes i) a length value to indicate a length of theregular data unit when the first subfield indicates that the packet isthe regular data unit and ii) a number of streams indicator when thefirst subfield indicates that the packet is the first NDP soundingpacket.
 25. A method according to claim 24, wherein the first subfieldis a modulation and coding (MCS) subfield, and a value of the MCSsubfield other than a valid MCS value is used to indicate that thepacket is a sounding packet, wherein the valid MCS value is a value usedto indicate a valid MCS for a regular data unit.
 26. An apparatuscomprising: a network interface configured to generate a regular dataunit that includes a data payload portion, wherein the regular data unitis to be transmitted in an extended range physical layer (PHY) mode,generate a signal field including generating a first subfield and asecond subfield, wherein the signal field is to be included in one of i)a preamble of the regular data unit or ii) a first null data packet(NDP) sounding packet to be transmitted in the extended range mode,generate a second NDP sounding packet according to a first PHY soundingpacket format specified by a communication protocol, wherein the secondNDP sounding packet is to be transmitted in a normal PHY mode, andgenerate the first NDP sounding packet according to a second PHYsounding packet format defined by the communication protocol, whereinthe first NDP sounding packet is to be transmitted in an extended rangePHY mode.
 27. An apparatus according to clam 26, wherein: the first PHYsounding packet format is based on a first PHY preamble format specifiedby the communication protocol to be included in data units transmittedin the normal PHY mode; and the second PHY sounding packet format isbased on a second PHY preamble format specified by the communicationprotocol to be included in data units transmitted in the extended rangePHY mode.
 28. An apparatus according to claim 27, wherein the second PHYpreamble format is specified for single stream data units, and whereinthe second PHY sounding packet format is specified for multi streamsounding packets.
 29. An apparatus according to claim 26, wherein: thefirst subfield is a length subfield i) set to a value other than a firstvalue when the signal field is to be included in the regular data unitand ii) set to the first value when the signal field is to be includedin the first NDP sounding packet; and the second subfield includes anumber of streams indicator when signal field is to be included in thefirst NDP sounding packet.
 30. An apparatus according to claim 26,wherein: the first subfield is a length subfield i) set to a value otherthan a first value when the signal field is to be included in theregular data unit and ii) set to the first value when the signal fieldis to be included in the first NDP sounding packet; and the secondsubfield includes i) a number of streams indicator when the signal fieldis to be included in the first NDP sounding packet and ii) a scramblerseed value when the signal field is to be included in the regular dataunit.
 31. An apparatus according to claim 26, wherein: the firstsubfield is set to indicate whether the packet is the regular datapacket or the first NDP sounding packet; and the second subfieldincludes i) a length value to indicate a length of the regular data unitwhen the first subfield indicates that the packet is the regular dataunit and ii) a number of streams indicator when the first subfieldindicates that the packet is the first NDP sounding packet.
 32. Anapparatus according to claim 31, wherein the first subfield is amodulation and coding scheme (MCS) subfield, and the network interfaceis configured to indicate that the packet is a sounding packet bysetting the MCS subfield to a value other than a valid MCS value,wherein the valid MCS value is a value used to indicate a valid MCS fora regular data unit.
 33. A method according to claim 1, wherein thesub-field is used as a reserved subfield in the signal field for regularpackets that are not NDP sounding packets.
 34. A method according toclaim 1, wherein the sub-field is part of a length subfield in thesignal field for regular packets that are not NDP sounding packets. 35.A method according to claim 1, wherein the sub-field is part of ascrambler seed subfield in the signal field for regular packets that arenot NDP sounding packets.
 36. An apparatus according to claim 10,wherein the sub-field is used as a reserved subfield in the signal fieldfor regular packets that are not NDP sounding packets.
 37. An apparatusaccording to claim 10, wherein the sub-field is part of a lengthsubfield in the signal field for regular packets that are not NDPsounding packets.
 38. An apparatus according to claim 10, wherein thesub-field is part of a scrambler seed subfield in the signal field forregular packets that are not NDP sounding packets.